Field
This disclosure relates to power converters, and specifically to semi-regulated voltage sources for use with asynchronous digital logic circuits.
Description of the Related Art
In this patent, the term “processor” means a digital circuit that performs some sequence of operations. A processor may typically, but not necessarily, execute stored instructions to accomplish its assigned function. Processors that typically execute stored instructions include microprocessors, microcontrollers, digital signal processors, and coprocessors. Processors that do not execute stored instructions include single-purpose processors such as encryption engines and fast Fourier transform engines. The sequence of operations performed by such engines may be controlled, for example, by a hardware state machine rather than stored instructions.
Most digital processors in use today are synchronous, which is to say various elements within the digital processor operate synchronously in response to a common clock signal. The power consumption of a synchronous processor depends on the complexity of the processor (i.e., the number of gates and other functional elements), the clock rate, and the operating voltage. In general, higher operating speed requires higher operating voltage. To minimize the power consumption of a synchronous digital logic circuit, the circuit may be operated at the lowest possible clock rate consistent with the circuit function and the lowest voltage that will support operation at that clock rate. The methodology and tools for designing synchronous logic circuits are well developed, so long as the processor circuit is designed to operate from a power supply voltage substantially above the threshold voltage of the transistors comprising the processor. However, to achieve the lowest possible power consumption, it may be preferable to operate a digital logic circuit at a voltage near or below the transistor threshold voltage. While research papers have shown that near-threshold operation of synchronous processors (i.e., operation with a power supply voltage near the transistor threshold voltage) may be possible, the delay of near-threshold and below-threshold logic gates may vary by a factor of up to 100 over an operating temperature range. Further, the delay may vary by a factor of five or more between gates at a single temperature. As a consequence, it is difficult, if not impossible, to estimate the minimum required clock frequency for near-threshold voltage operation of synchronous logic circuits.
Asynchronous processors circuits do not operate from a common clock signal, such that the delay of an asynchronous processor is determined solely by the cumulative delay of the gates and other logic elements within the asynchronous processor. Asynchronous processors are typically operated in a cyclic manner. A cycle is initiated when input data is provided to the processor. The processor then performs some operation upon the input data, with the time required to perform the operation determined by the accumulated delays of the logic circuits within the processor. When the operation is completed, and all of the outputs of the processor have assumed their final values, a feedback or acknowledge signal may be generated to indicate completion of the current processing cycle and readiness to begin the next cycle.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number where the element is introduced and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.